Stabilizing Cu 2+ Ions by Solid Solutions to Promote CO 2 Electroreduction to Methane.

Copper is the only metal catalyst that can perform the electrocatalytic CO 2 reduction reaction (CRR) to produce hydrocarbons and oxygenates. Its surface oxidation state determines the reaction pathway to various products. However, under the cathodic potential of CRR conditions, the chemical composition of most Cu-based catalysts inevitably undergoes electroreduction from Cu 2+ to Cu 0 or Cu 1+ species, which is generally coupled with phase reconstruction and the formation of new active sites. Since the initial Cu 2+ active sites are hard to retain, there have been few studies about Cu 2+ catalysts for CRR. Herein we propose a solid-solution strategy to stabilize Cu 2+ ions by incorporating them into a CeO 2 matrix, which works as a self-sacrificing ingredient to protect Cu 2+ active species. In situ spectroscopic characterization and density functional theory calculations reveal that compared with the conventionally derived Cu catalysts with Cu 0 or Cu 1+ active sites, the Cu 2+ species in the solid solution (Cu-Ce-O x ) can significantly strengthen adsorption of the *CO intermediate, facilitating its further hydrogenation to produce CH 4 instead of dimerization to give C 2 products. As a result, different from most of the other Cu-based catalysts, Cu-Ce-O x delivered a high Faradaic efficiency of 67.8% for CH 4 and a low value of 3.6% for C 2 H 4 .